1 /*
2 * Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25 package java.util;
26
27 import java.util.function.LongConsumer;
28 import java.util.function.LongSupplier;
29 import java.util.function.Supplier;
30 import java.util.stream.LongStream;
31
32 /**
33 * A container object which may or may not contain a {@code long} value.
34 * If a value is present, {@code isPresent()} returns {@code true}. If no
35 * value is present, the object is considered <i>empty</i> and
36 * {@code isPresent()} returns {@code false}.
37 *
38 * <p>Additional methods that depend on the presence or absence of a contained
39 * value are provided, such as {@link #orElse(long) orElse()}
40 * (returns a default value if no value is present) and
41 * {@link #ifPresent(LongConsumer) ifPresent()} (performs an
42 * action if a value is present).
43 *
44 * <p>This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
45 * class; programmers should treat instances that are
46 * {@linkplain #equals(Object) equal} as interchangeable and should not
47 * use instances for synchronization, or unpredictable behavior may
48 * occur. For example, in a future release, synchronization may fail.
49 *
50 * @apiNote
51 * {@code OptionalLong} is primarily intended for use as a method return type where
52 * there is a clear need to represent "no result." A variable whose type is
53 * {@code OptionalLong} should never itself be {@code null}; it should always point
54 * to an {@code OptionalLong} instance.
55 *
56 * @since 1.8
57 */
58 @jdk.internal.ValueBased
59 @jdk.internal.MigratedValueClass
60 public final class OptionalLong {
61 /**
62 * Common instance for {@code empty()}.
63 */
64 private static final OptionalLong EMPTY = new OptionalLong();
65
66 /**
67 * If true then the value is present, otherwise indicates no value is present
68 */
69 private final boolean isPresent;
70 private final long value;
71
72 /**
73 * Construct an empty instance.
74 *
75 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
76 * should exist per VM.
77 */
78 private OptionalLong() {
79 this.isPresent = false;
80 this.value = 0;
81 }
82
83 /**
84 * Returns an empty {@code OptionalLong} instance. No value is present for
85 * this {@code OptionalLong}.
86 *
87 * @apiNote
88 * Though it may be tempting to do so, avoid testing if an object is empty
89 * by comparing with {@code ==} or {@code !=} against instances returned by
90 * {@code OptionalLong.empty()}. There is no guarantee that it is a singleton.
91 * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
92 *
93 * @return an empty {@code OptionalLong}.
94 */
95 public static OptionalLong empty() {
96 return EMPTY;
97 }
98
99 /**
100 * Construct an instance with the described value.
101 *
102 * @param value the long value to describe
103 */
104 private OptionalLong(long value) {
105 this.isPresent = true;
106 this.value = value;
107 }
108
109 /**
110 * Returns an {@code OptionalLong} describing the given value.
111 *
112 * @param value the value to describe
113 * @return an {@code OptionalLong} with the value present
114 */
115 public static OptionalLong of(long value) {
116 return new OptionalLong(value);
117 }
118
119 /**
120 * If a value is present, returns the value, otherwise throws
121 * {@code NoSuchElementException}.
122 *
123 * @apiNote
124 * The preferred alternative to this method is {@link #orElseThrow()}.
125 *
126 * @return the value described by this {@code OptionalLong}
127 * @throws NoSuchElementException if no value is present
128 */
129 public long getAsLong() {
130 if (!isPresent) {
131 throw new NoSuchElementException("No value present");
132 }
133 return value;
134 }
135
136 /**
137 * If a value is present, returns {@code true}, otherwise {@code false}.
138 *
139 * @return {@code true} if a value is present, otherwise {@code false}
140 */
141 public boolean isPresent() {
142 return isPresent;
143 }
144
145 /**
146 * If a value is not present, returns {@code true}, otherwise
147 * {@code false}.
148 *
149 * @return {@code true} if a value is not present, otherwise {@code false}
150 * @since 11
151 */
152 public boolean isEmpty() {
153 return !isPresent;
154 }
155
156 /**
157 * If a value is present, performs the given action with the value,
158 * otherwise does nothing.
159 *
160 * @param action the action to be performed, if a value is present
161 * @throws NullPointerException if value is present and the given action is
162 * {@code null}
163 */
164 public void ifPresent(LongConsumer action) {
165 if (isPresent) {
166 action.accept(value);
167 }
168 }
169
170 /**
171 * If a value is present, performs the given action with the value,
172 * otherwise performs the given empty-based action.
173 *
174 * @param action the action to be performed, if a value is present
175 * @param emptyAction the empty-based action to be performed, if no value is
176 * present
177 * @throws NullPointerException if a value is present and the given action
178 * is {@code null}, or no value is present and the given empty-based
179 * action is {@code null}.
180 * @since 9
181 */
182 public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {
183 if (isPresent) {
184 action.accept(value);
185 } else {
186 emptyAction.run();
187 }
188 }
189
190 /**
191 * If a value is present, returns a sequential {@link LongStream} containing
192 * only that value, otherwise returns an empty {@code LongStream}.
193 *
194 * @apiNote
195 * This method can be used to transform a {@code Stream} of optional longs
196 * to an {@code LongStream} of present longs:
197 * <pre>{@code
198 * Stream<OptionalLong> os = ..
199 * LongStream s = os.flatMapToLong(OptionalLong::stream)
200 * }</pre>
201 *
202 * @return the optional value as an {@code LongStream}
203 * @since 9
204 */
205 public LongStream stream() {
206 if (isPresent) {
207 return LongStream.of(value);
208 } else {
209 return LongStream.empty();
210 }
211 }
212
213 /**
214 * If a value is present, returns the value, otherwise returns
215 * {@code other}.
216 *
217 * @param other the value to be returned, if no value is present
218 * @return the value, if present, otherwise {@code other}
219 */
220 public long orElse(long other) {
221 return isPresent ? value : other;
222 }
223
224 /**
225 * If a value is present, returns the value, otherwise returns the result
226 * produced by the supplying function.
227 *
228 * @param supplier the supplying function that produces a value to be returned
229 * @return the value, if present, otherwise the result produced by the
230 * supplying function
231 * @throws NullPointerException if no value is present and the supplying
232 * function is {@code null}
233 */
234 public long orElseGet(LongSupplier supplier) {
235 return isPresent ? value : supplier.getAsLong();
236 }
237
238 /**
239 * If a value is present, returns the value, otherwise throws
240 * {@code NoSuchElementException}.
241 *
242 * @return the value described by this {@code OptionalLong}
243 * @throws NoSuchElementException if no value is present
244 * @since 10
245 */
246 public long orElseThrow() {
247 if (!isPresent) {
248 throw new NoSuchElementException("No value present");
249 }
250 return value;
251 }
252
253 /**
254 * If a value is present, returns the value, otherwise throws an exception
255 * produced by the exception supplying function.
256 *
257 * @apiNote
258 * A method reference to the exception constructor with an empty argument
259 * list can be used as the supplier. For example,
260 * {@code IllegalStateException::new}
261 *
262 * @param <X> Type of the exception to be thrown
263 * @param exceptionSupplier the supplying function that produces an
264 * exception to be thrown
265 * @return the value, if present
266 * @throws X if no value is present
267 * @throws NullPointerException if no value is present and the exception
268 * supplying function is {@code null}
269 */
270 public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
271 if (isPresent) {
272 return value;
273 } else {
274 throw exceptionSupplier.get();
275 }
276 }
277
278 /**
279 * Indicates whether some other object is "equal to" this
280 * {@code OptionalLong}. The other object is considered equal if:
281 * <ul>
282 * <li>it is also an {@code OptionalLong} and;
283 * <li>both instances have no value present or;
284 * <li>the present values are "equal to" each other via {@code ==}.
285 * </ul>
286 *
287 * @param obj an object to be tested for equality
288 * @return {@code true} if the other object is "equal to" this object
289 * otherwise {@code false}
290 */
291 @Override
292 public boolean equals(Object obj) {
293 if (this == obj) {
294 return true;
295 }
296
297 return obj instanceof OptionalLong other
298 && (isPresent && other.isPresent
299 ? value == other.value
300 : isPresent == other.isPresent);
301 }
302
303 /**
304 * Returns the hash code of the value, if present, otherwise {@code 0}
305 * (zero) if no value is present.
306 *
307 * @return hash code value of the present value or {@code 0} if no value is
308 * present
309 */
310 @Override
311 public int hashCode() {
312 return isPresent ? Long.hashCode(value) : 0;
313 }
314
315 /**
316 * Returns a non-empty string representation of this {@code OptionalLong}
317 * suitable for debugging. The exact presentation format is unspecified and
318 * may vary between implementations and versions.
319 *
320 * @implSpec
321 * If a value is present the result must include its string representation
322 * in the result. Empty and present {@code OptionalLong}s must be
323 * unambiguously differentiable.
324 *
325 * @return the string representation of this instance
326 */
327 @Override
328 public String toString() {
329 return isPresent
330 ? ("OptionalLong[" + value + "]")
331 : "OptionalLong.empty";
332 }
333 }